Fix name ambiguity in trait object diagram

[mgeisler]

So if <Dog as Pet>::name refers to the field name in the Dog struct, what does <Cat as Pet>::name refer to?

Oh, sorry, I misunderstood above. <Dog as Pet>::name is supposed to refer to the Dog::name method.

If you called the field dogname (in the Dog struct) I think it would be clearer what's going on. Then, presumably, the label would become <Dog as Pet>::dogname.

It would make more sense if the ::name refers to the function (though the function isn't really on heap, presumably and the name: Fido would then be dogname: Fido.

Yeah, that is what the picture was supposed to show. I think "the heap" as "somewhere in memory". I guess the vtable is generated at compile-time and put somewhere in the binary — and then memory-mapped into the address space when the program is loaded from disk.

Obviously, I'm confused, but I don't think adding this information to the notes would help, because the information still seems inconsistent to me. (Sorry.)

No, I actually think you got it!

I suggest we change the name method to talk or speak in the Pet trait. The implementations can then be something like

impl Pet for Cat {
    fn speak(&self) -> String {
        String::from("Miau!")
    }
}

impl Pet for Dog {
    fn speak(&self) -> String {
        format!("Woof, my name is {}!", self.name);
    }
}

That would remove the name ambiguity. We should then also write notes to explain each part of the diagram.

Originally posted by @mgeisler in #1270 (reply in thread)